ath9k_hw: fix LNA control on WLAN sleep

When WLAN enter full sleep mode, WLAN HW should send out a LNA_TAKE
message for BT to take control of the shared LNA. Otherwise BT traffic
is completely stopped whenever the wlan interface is moved full sleep
mode.

Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>